U.S. patent number 5,327,048 [Application Number 08/023,534] was granted by the patent office on 1994-07-05 for bi-level lighting control system for hid lamps.
This patent grant is currently assigned to North American Philips Corporation. Invention is credited to Patrick E. Troy.
United States Patent |
5,327,048 |
Troy |
July 5, 1994 |
Bi-level lighting control system for hid lamps
Abstract
A bi-level control system includes a plurality of slave units,
each for connection to a respective ballast and HID lamp of a
plurality of HID lighting fixtures, and a common control unit. Each
slave unit includes a switched capacitor and a slave relay which
has one input connectable to a common line of an AC power supply
branch circuit powering the fixtures and another input adapted for
receiving a line voltage signal. The control unit includes an
output connected to the control inputs of each of the slave units
by a single control line and switchably connected to line voltage.
Dimming of the HID lamp is accomplished by switching line voltage
to the output of the control unit which causes the slave relay to
switch the slave capacitor into circuit with the HID lamp and
ballast. Use of a single control line connecting each of the slave
units to the control unit greatly reduces wiring over known
systems. The control unit is also adapted to receive a control
input from a sensor via a single input line, further reducing
wiring.
Inventors: |
Troy; Patrick E. (Chicago,
IL) |
Assignee: |
North American Philips
Corporation (New York, NY)
|
Family
ID: |
21815686 |
Appl.
No.: |
08/023,534 |
Filed: |
February 26, 1993 |
Current U.S.
Class: |
315/240; 315/244;
315/291; 315/DIG.4; 315/311 |
Current CPC
Class: |
H05B
47/115 (20200101); H05B 41/42 (20130101); H05B
47/18 (20200101); Y10S 315/04 (20130101) |
Current International
Class: |
H05B
41/38 (20060101); H05B 41/42 (20060101); H05B
37/02 (20060101); H05B 041/42 () |
Field of
Search: |
;315/240,159,244,284,291,311,DIG.4 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
0447136 |
|
Mar 1991 |
|
EP |
|
8905536 |
|
May 1989 |
|
WO |
|
2213983 |
|
Aug 1989 |
|
GB |
|
Primary Examiner: Bertsch; Richard A.
Assistant Examiner: Scheuermann; David W.
Attorney, Agent or Firm: Wieghaus; Brian J.
Claims
I claim:
1. A bi-level control system for an HID lighting system having (i)
an AC power supply branch circuit with a line voltage line and a
common line and (ii) a luminaire including an HID lamp and a
ballast means connected to the HID lamp and to the line voltage and
common lines for providing stable operating power to the lamp, said
control system comprising:
capacitance switching means for switching a capacitance into and
out of circuit with said HID lamp and ballast means to switch said
HID lamp between a first light output level and a second, different
light output level, said capacitance switching means having a pair
of control inputs; and
control means including an output switchably connectable to a
source of electric potential such that, with one of said control
inputs of said capacitance switching means connected to the common
line of the AC branch circuit and the other said control input of
the capacitance switching means connected to said output of said
control means with a single control line, said control means is
effective to control the switching of said capacitance switching
means with the single control line by switching of the source of
electric potential to said output of said control means.
2. A bi-level control system according to claim 1, wherein said
control means includes an input connectable to the line voltage
line of the AC branch circuit, the electric potential switchable to
said output of said control means being line voltage.
3. A bi-level control system according to claim 2, wherein said
capacitance switching means includes a switched slave capacitor and
a slave relay which includes said control inputs, and said control
means includes a control relay having a first switch position
connecting said input and output of said control means such that a
circuit is completed between said input of said control means,
through said control relay, through said control line and control
inputs of said slave relay to said common line for switching said
slave relay to switch said lamp between said first and second light
output levels.
4. A bi-level control system according to claim 3, wherein said
slave relay is an electro-mechanical relay having a moveable switch
member moveable between first and second switch positions and an
energizeable coil connected between said control inputs for moving
said switch member.
5. A bi-level control system according to claim 4, wherein said
capacitance switching means further comprises surge suppression
means for suppressing current surges across said slave relay.
6. A bi-level control system according to claim 1, wherein said
control means includes means for receiving a control input on a
single input line.
7. A bi-level control system according to claim 6, wherein said
means for receiving a control input comprises an optoisolator
having a pair of inputs, one of said inputs being connected to a
common line within said control unit connectable to the common line
of the AC branch circuit and the other optoisolator input being
connectable to the single input line.
8. A bi-level HID control system for connection to an HID lighting
system having (i) an AC power supply branch circuit having a common
line and a line voltage line and (ii) at least one HID luminaire,
the luminaire including an HID lamp and ballast circuit connected
thereto for controlling the operating current through the lamp, the
ballast circuit having an inductance and a ballast capacitance
connected in series with the lamp, a pair of power input leads each
connected to a respective one of the common and line voltage lines
of the branch circuit, and a pair of output leads, including one
lead connected to the ballast capacitance, for connection to the
lamp, said bi-level control system comprising:
a) a control unit comprising
i) an input for connection to the line voltage line,
ii) an output, and
iii) control means for switchably connecting said output to said
input, and
b) a slave unit for connection in the HID luminaire, said slave
unit comprising
i ) a slave capacitance, and
ii) an electro-mechanical slave relay for switching said slave
capacitance into and out of the ballast circuit in the luminaire,
said slave relay including a moveable switch member moveable
between first and second switch positions and a coil energizeable
for moving said switch member,
iii) a first lead connected to one side of said coil for connection
to the common line of the branch circuit,
iv) a second lead connected to the other side of said coil for
connection to said output of said control unit, said second lead
being connectable to said output with a single control line,
v) a third lead connected to one side of said slave capacitance for
connection to the one of the pair of ballast circuit output leads
connected to the ballast capacitance,
vi) a fourth lead connected to the other side of said slave
capacitance for connection to the lamp in the luminaire,
with said leads of said slave unit respectively connected to said
output of said control unit, the common and line voltage lines of
the branch circuit, and ballast, said coil of said slave relay is
responsive to a line voltage signal received on said second lead
from said output of said control unit to move said switch member
for one of (a) switching said slave capacitance into the ballast
circuit and (b) switching said slave capacitance out of the ballast
circuit, whereby the light output level of the HID lamp is switched
from a first light output level to a second, different light output
level.
9. A bi-level lighting control system according to claim 8, wherein
said control unit includes a pair of power inputs each connectable
to a respective one of the neutral and line voltage lines of the
branch circuit, and said control means comprises
i) a switching means comprised of a master electro-mechanical
control relay having a normally open switch position and a closed
switch position, in said closed position said control relay
connecting said line voltage input to said output of said control
unit and
ii) switching control means for switching said control relay
between said normally open switch position and said closed switch
position, in said closed position the line voltage signal in said
output of said control unit switching said slave relay from said
normally closed to said open position.
10. A bi-level lighting control system according to claim 8,
wherein said control system comprises a plurality of said slave
units, said second lead of one of said slave units being
connectable to said output of said slave unit, and said second lead
of each successive additional control unit being connectable to
said second lead of each prior slave unit, and with said slave
units so connected each of said capacitance switching means of said
slave units is responsive to the line voltage signal on the output
of said control unit.
11. A bi-level lighting control system according to claim 8,
wherein said first switch position of said slave relay is normally
closed and said second switch position is normally open, and said
slave relay is connected to said slave capacitance and said leads
of said slave unit such that with said slave relay in said normally
closed switch position said slave capacitance is disconnected from
the ballast capacitance and in the open position of said slave
relay said slave capacitance is electrically connected with said
ballast capacitance and HID lamp, whereby in said open switch
position of said slave relay the HID lamp operates at a reduced
light output level reduced with respect to the light output level
in the closed switch position of said slave relay when said slave
capacitance is not switched in said ballast circuit.
12. A bi-level lighting control system according to claim 11,
wherein said slave capacitance is a single capacitor component, and
wherein for connection of said slave unit to a ballast circuit in
which the ballast capacitance consists of a single capacitor
component having a rated voltage, said capacitor component in said
slave unit has a lower rated voltage than the rated voltage of the
capacitor component in the ballast circuit.
13. A bi-level lighting control system according to claim 12,
wherein said slave unit further includes a surge suppressor
connected to said slave capacitor and said electro-mechanical slave
relay for protecting said slave relay from current surges from
discharging of said slave capacitor upon the switching of said
slave capacitor out of the ballast circuit by said slave relay.
14. A bi-level lighting control system according to claim 13,
wherein said slave unit includes a housing in which said slave
capacitor, slave relay, and surge suppressor are enclosed, said
slave leads extending from said housing for connection to the
common line of the branch circuit, the control line from said
output of said control unit, the one of the ballast leads connected
to the ballast capacitance, and a lamp terminal of the HID
lamp.
15. A bi-level lighting control system according to claim 11,
wherein:
said control means comprises
i) switching means comprised of an electro-mechanical control relay
having a normally open switch position and a closed switch
position, and
ii) switching control means for switching said control relay
between said normally open switch position and said closed switch
position, in said closed position said output of said control unit
being connected to said input of said control unit such that line
voltage appears on said output and said slave relay is switched
from said normally closed to said open switch position.
16. A bi-level lighting control system according to claim 15,
wherein said switching control means further comprises input
receiving means for receiving AC or DC input signals,
said switching control means being responsive to an input signal
received by said input receiving means for controlling switching of
said master relay.
17. A bi-level control system according to claim 16, wherein said
input receiving means comprises an optoisolator having a pair of
inputs, one of said inputs being connected to a common line within
said control unit and the other being connectable to a single input
line.
18. A bi-level lighting control system according to claim 16,
wherein said control means further includes timing means coupled to
said switching control means for preventing switching of said
control relay from said open position to said closed position
within a predetermined time period after AC power is supplied to
the branch circuit, whereby said slave relay remains in the
normally closed position with the slave capacitance disconnected
from the ballast circuit during said predetermined time period.
19. A bi-level lighting control system according to claim 16,
wherein:
said timing means includes an output, said output having a first
logic state indicative of the predetermined time period not having
been reached and a second logic state indicative of the
predetermined time having been reached;
said input receiving means comprises an optoisolator having an
output with a first logic state indicative of a signal not being
received and a second logic state indicative of a signal having
been received; and
said switching control means further includes a plurality of logic
gates connected to said outputs of said timing means and said input
receiving means for controlling the switch position of said master
relay.
20. A slave unit of a bi-level control system for connection in an
HID luminaire having (i) an HID lamp and (ii) a ballast circuit
including a ballast capacitance connected to said lamp for
controlling the lamp operating current, said slave unit
comprising:
i) a slave capacitance
ii) and electro-mechanical slave relay for switching said slave
capacitance into and out of the ballast circuit in the luminaire,
said slave relay including a moveable switch member moveable
between a normally closed and an open switch position and a coil
energizeable for moving said switch member,
iii) a first lead connected to one side of said coil for connection
to a common, neutral line of an AC power supply branch circuit,
iv) a second lead connected to the other side of said coil for
connection to a switchable line voltage output of a control unit of
the control system, said second lead being connectable to said
output of the control unit with a single control line,
v) a third lead connected to one side of said slave capacitance for
connection to an output lead of the ballast circuit output
connected to the ballast capacitance, and
vi) a fourth lead connected to the other side of the slave
capacitance for connection to the lamp in the luminaire,
with said leads of said slave unit respectively connected to the
switchable line voltage output of the control unit, the common and
line voltage lines of the branch circuit, and the ballast, said
slave relay is responsive to a line voltage signal received on said
second lead from said output of said control unit for one of (a)
switching said slave capacitance into the ballast circuit and (b)
switching said slave capacitance out of the ballast circuit,
whereby the light output level of the HID lamp is switched from a
first light output level to a second, different light output
level.
21. A slave unit according to claim 20, wherein said slave relay is
connected to said slave capacitance and said leads of said slave
unit such that with said slave relay in said normally closed switch
position said slave capacitance is disconnected from the ballast
capacitance and in the open position of said slave relay said slave
capacitance is electrically connected with said ballast and HID
lamp, whereby in said open switch position of said slave relay the
HID lamp operates at reduced light output level reduced with
respect to the light output level in the closed switch position of
said slave relay when said slave capacitance is not switched in
said ballast circuit.
22. A slave unit according to claim 21, wherein said slave
capacitance is a single capacitor component, and wherein for
connection of said slave unit to a ballast circuit in which the
ballast capacitance consists of a single capacitor component having
a rated voltage, said capacitor component in said slave unit has a
lower rated voltage than the rated voltage of the capacitor
component in the ballast circuit.
23. A slave unit according to claim 22, wherein said slave unit
further includes a surge suppressor connected to said slave
capacitor and said electro-mechanical slave relay for protecting
said slave relay from current surges from discharging of said slave
capacitor upon the switching of said slave capacitor out of the
ballast circuit by said slave relay.
24. A slave unit according to claim 23, further comprising a
housing in which said slave capacitor, slave relay, and surge
suppressor are enclosed, said slave leads extending from said
housing for connection to the common line of the branch circuit,
the control line from the output of the control unit, the one of
the ballast leads connected to the ballast capacitance, and a lamp
terminal of the HID lamp.
25. A control unit of a bi-level HID control system having a slave
unit with a switched capacitor and a slave relay connected thereto,
the slave relay being switchable with a line voltage signal
received on a control input thereof, said control unit
comprising:
i) a pair of power inputs each connectable to a respective one of
the common and line voltage lines of an AC power supply branch
circuit;
ii) a control output;
iii) switching means comprised of an electro-mechanical control
relay having first and second switch positions, in only one of said
switch positions said control output being connected to said power
input connectable to the line voltage line; and
iii) switching control means for switching said control relay
between said switch positions to control the connection of the line
voltage line to the output, whereby switching of the slave relay is
controlled when its control input is connected to said control
output of said control unit with a single control line.
26. A control unit according to claim 25, wherein said control unit
further comprises input receiving means for receiving AC or DC
input signals, and
said switching control means is responsive to an input signal
received by said input receiving means for switching said control
relay.
27. A control unit according to claim 26, further comprising timing
means coupled to said switching control means for preventing
switching of said master relay within a predetermined time period
after AC power is supplied to the branch circuit.
28. A control unit according to claim 27, wherein:
said timing means includes an output, said output having a first
logic state indicative of the predetermined time period not having
been reached and a second logic state indicative of the
predetermined time having been reached;
said input receiving means comprises an optoisolator having an
output with a first logic state indicative of a signal not being
received and a second logic state indicative of a signal having
been received; and
said switching control means includes a plurality of logic gates
connected to said outputs of said timing means and said
optoisolator for controlling the switch position of said control
relay.
29. A bi-level HID lighting system including an AC power supply
branch circuit having a line voltage line and a common line, at
least one HID lamp, a ballast means connected to said HID lamp and
said line voltage and common lines for providing stable operating
power to said lamp, a switched slave capacitance, a slave relay for
switching said slave capacitance into and out of circuit with said
HID lamp and ballast means to switch said HID lamp between a first
light output level and a second different light output level, said
slave relay having a pair of control inputs, and a control unit
connected to said slave relay for controlling the switching of said
slave relay, wherein the improvement comprises:
one of said control inputs of said slave relay is connected to said
common line of said AC branch circuit;
said control unit includes switch means for switchably connecting
the line voltage line to an output of the control unit; and
a single control line connects said output of said control unit to
the other of said control inputs of said slave relay, whereby
switching of said line voltage line to said output of said control
unit switches said slave relay and one of a) connects the slave
capacitance in circuit with said ballast and HID lamps and b)
disconnects said slave capacitance from said ballast and HID lamp,
whereby the light output level of the HID lamp is switched between
the first and second, different output levels.
30. A bi-level HID lighting system according to claim 29, wherein
said control unit includes a power input for connection to said
line voltage line of said AC power supply branch circuit, and said
control relay includes a first switch position connecting said
power input of said control unit and said output of said control
relay such that a circuit is completed between said power input of
said control unit, through said control relay, through said control
line and control inputs of said slave relay to said common line for
switching said slave relay to switch said lamp between said first
and second light output levels.
31. A bi-level HID lighting system according to claim 30, wherein
said slave relay is an electro-mechanical relay having switch
contacts, a moveable switch member moveable between first and
second switch positions against said switch contacts, and a coil
connected between said control inputs of said slave unit for moving
said switch member, said coil being energized with said control
relay in said first switch position such that said switched
capacitor is switched into series with said ballast means and HID
lamp.
32. A bi-level HID lighting system according to claim 31, further
comprising surge suppression means for suppressing current surges
across said switch contacts and switch member by discharging of
said switched capacitance upon switching of said switched
capacitance out of circuit with said ballast means and HID
lamp.
33. A bi-level HID lighting system according to claim 29, wherein
said control unit includes means for receiving a control input on a
single input line.
34. A bi-level HID lighting system according to claim 33, wherein
said means for receiving a control input comprises an optoisolator
having a pair of control inputs, one of said control inputs being
connected to a common line within said control unit and the other
being connected to a single input line.
Description
BACKGROUND OF THE INVENTION
1) Field of the Invention
The invention relates to a bi-level control system for operating
high intensity discharge lamps at a first light output level and a
second, reduced light output level, and more particularly, to
improvements in such a control system which employs a switched
capacitor for regulating the power supplied to the lamps. The
invention also relates to an HID lighting system having such a
control system and to components of the control system.
2) Description of the Prior Art
High intensity discharge (HID) lamps include, for example, mercury
vapor, metal halide, and high pressure sodium discharge lamps.
These lamps are operated with a ballast circuit to control the lamp
operating current because of the negative voltage-current
characteristics of the discharge arc within these lamps.
Conventionally, electromagnetic transformer ballasts having a
series connected inductance and capacitance (L-C circuit) in the
form of a choke and capacitor, have been employed for this
purpose.
Typically, the ballast, HID lamp, and reflector are combined into a
fixture, or luminaire. For general illumination of, for example,
warehouses and factories, a large number of luminaires are
suspended form a ceiling. Generally, a plurality of the luminaires
are connected in an alternating current (AC) power supply branch
circuit and controlled by a single switch or circuit breaker which
is effective to switch all of the lamps between an "off" state, in
which the lamps are completely extinguished, and an "on" state in
which the lamps are operated at full rated power.
Recently, because of energy saving considerations, it has become
desirable in other types of lighting systems, for example
fluorescent lighting, to employ more sophisticated controls such as
occupancy sensors to turn the lamps off when nobody is present in a
room and to turn the lights on when someone enters. However, this
is not practical for HID lamps, which typically require several
minutes to ignite, warm-up and reach their full light output
levels. Additionally, most HID lamps have hot re-strike problems
which makes it difficult to re-ignite the lamp shortly after being
turned off while they still remain at an elevated temperature. With
some lamp-ballast combinations it may take up to approximately ten
minutes after a lamp has been turned off before it will re-ignite.
Thus, employing a control system which turns HID lamps completely
off when someone leaves the lighted space is not feasible because
the lamps will not provide sufficient light quickly enough if
someone re-enters the space shortly thereafter.
However, if HID lamps are operated at a reduced power level,
instead of being completely turned off, they will return to a full
or near full output level within an acceptable period of time. U.S.
Pat. No. 4,994,718 (Gordin) shows such a system and employs a
conventional electromagnetic ballast having a series L-C circuit.
The light output from the lamp is changed by switching the
capacitance in series with the lamp between a first valve which
provides a full light output level and a second, reduced valve
which lowers the power to the lamp and provides a reduced,
energy-saving light output level. For this purpose, a second,
switched capacitor is provided in addition to the single capacitor
normally employed in the ballast circuit. The two capacitors may be
arranged in series or parallel with each other, with one of the
capacitors being switched into or out of circuit with the other
capacitor to change the capacitance of the L-C circuit.
Gordin's switch for switching the switched capacitor into and out
of the ballast circuit is a single electro-mechanical slave relay
provided in a ballast housing which contains ballasts and switched
capacitors for several lamps. A second electro-mechanical control
relay in a separate controller remote from the ballast housing is
connected to the slave relay in each ballast housing. A mechanical
toggle switch, switchable between a high and low position, controls
the position of the control relay, which in turn controls the
position of the slave relays to switch the switched capacitors into
and out of the ballast circuit to change the light output of their
respective lamps.
A disadvantage of the Gordin system, however, is that control of
the slave relays is accomplished by a pair of power supply wires
connected between the control relay and the slave relay, in
addition to the pair of power supply wires used to supply power to
the ballasts. Furthermore, one slave relay is used to control the
switched capacitor of each of the several ballast circuits
contained in a ballast housing. While a common relay might be
favorable for the system in Gordin where several ballasts are
disposed in a common housing, this is usually not the case. Rather,
the more common arrangement is for each lamp and ballast to be in
included in a luminaire, or fixture, several of which are spaced
from each other in a ceiling. In this type of arrangement, a slave
relay common to several luminaires is not practical because of the
additional wiring needed to connect the slave relay and switched
capacitors to each of the spaced luminaires. For the same reason,
the use of an additional pair of power supply wires to connect the
control and slave relays, separate from the power supply wires
connecting the ballasts, is a disadvantage because of the extra
wiring, which is costly in terms of materials as well as labor for
installation. Additionally, the switch contacts of the
electro-mechanical relay in Gordin are subject to damage from
current surges by discharging of the switched capacitor when it is
switched out of the L-C ballast circuit.
U.S. Pat. No. 4,931,701 (Carl) shows another bi-level control
system which employs a switched capacitor. Instead of an
electro-mechanical slave relay as in Gordin, a solid state
zero-crossing relay is used. The zero-crossing relay is said to
ensure that the switching-in or switching-out of the switched
capacitor is timed to occur at a zero-crossing point of the applied
voltage. This applies or removes the switched capacitor only when
the voltage level is not able to cause excessive voltage spikes or
surges by the switched capacitor if it is partly or fully charged
when switched, which can cause damage to other components in the
circuit.
A disadvantage of such a solid state relay is that it allows a
small current flow to the switched capacitor when the relay is not
specifically switched for dimming the lamp. The small current flow
to the switched capacitor was found to cause unintentional dimming
of the lamp from the full light output level. It has also been
found that such a relay can false trigger and close at times other
than zero-crossing of the input voltage to the lamp. Additionally,
solid state relays are relatively expensive as compared to
electro-mechanical relays. Furthermore, a pair of control input
lines is connected directly to a pair of control inputs of the
solid state relay. As in Gordin, the use of an additional pair of
control wires connecting the relays is a distinct disadvantage.
As compared to more expensive systems that employ solid state
ballast circuitry to provide variable dimming of HID lamps over a
range of light levels, operation of HID lamps at only two or
several discrete light levels by switching of a switched capacitor
as in Gordin and Carl offers a cost effective alternative for
achieving energy savings. However, it is desirable to improve upon
these known implementations.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a control system having
a switched capacitor for operating an HID lamp at a first light
output level and at least a second, reduced light output level in
which the wiring of the relays is achieved more economically than
in the known systems.
It is another object of the invention to provide such a system in
which the ballast and relay components are protected from current
surges, upon the switching out of the switched capacitor, without
employing solid state zero-crossing relays for the switching of the
switched capacitor.
It is another object of the invention to provide such a control
system with components which can be readily retrofit to existing
luminaires which employ conventional electromagnetic ballasts
having a series L-C circuit, such as in constant-wattage
auto-transformer ballasts or regulated lag ballasts.
According to a first aspect of the invention, a bi-level HID
control system, for connection to an HID lighting system having (i)
an AC power supply branch circuit having a common, neutral line and
a line voltage line and (ii) an HID lamp and a ballast connected to
the lamp and to the common and line voltage lines, includes
capacitive switching means for switching a capacitance into and out
of circuit with the HID lamp and ballast means to switch the lamp
between a first and second, different output level and a control
means for controlling the capacitance switching means. The
capacitance switching means includes a pair of control inputs and
the control means includes an output switchably connected to a
source of electric potential. With one of the inputs of the
capacitance switching means connected to the common line of the AC
branch circuit and the other of the control inputs connected to the
output of the control means with a single control line, the control
means is effective to control the switching of said capacitance
switching means with the single control line by switching the
source of electric potential to the output of the control
means.
Since the capacitance switching means is connected to the same
common line as the ballast and only a single control line connects
the capacitance switching means to the control means, significantly
less wiring is needed than in the prior art systems of Gordin '718
and Carl '701.
In a favorable embodiment, the source of electric potential is line
voltage provided at an input of the control means which is
connected to the line voltage line of the branch circuit.
In another aspect of the invention, the capacitance switching means
includes an electro-mechanical slave relay switchable between a
normally closed switch position and an open switch position. The
slave relay is connected to the switched slave capacitance such
that in the normally closed switch position, the slave capacitance
is disconnected from the ballast capacitance and in the open
position, the slave capacitance is electrically connected in series
with the capacitor of the ballast L-C circuit and the HID lamp. The
control means includes a control relay having a switch position
connecting the input and output of the control means such that a
circuit is completed between the line voltage input of the control
means, through the control relay, through the control line and
control inputs of the slave relay to the common line for switching
the slave relay to switch the lamp between light levels.
Preferably, the switched slave capacitance is a single capacitor
component. For a ballast in which the capacitance of the L-C
ballast circuit consists of a single capacitor, the single slave
capacitor may have a lower rated voltage than the rated voltage of
the capacitor component in the ballast because of the series
connection when the slave relay is in the closed position. This
enables a capacitor component to be selected for the slave unit
which is physically of smaller size, than if, for example, the
slave capacitor were connected in parallel with the ballast
capacitor.
According to another aspect of the invention, a surge suppressor is
connected to the slave capacitor and the electro-mechanical slave
relay for protecting the switch contacts of the slave relay from
current surges by discharging of the slave capacitor upon the
switching of the slave capacitor out of the ballast circuit. Thus,
an electro-mechanical relay can be used which is less costly than a
solid state relay and is protected from voltage surges in a simple,
cost effective manner.
In a favorable embodiment, the slave capacitor, slave relay and
surge suppressor are provided in a housing to form a slave unit or
module. Four lead wires extend from the module: a first lead for
connection to the common line of the AC power supply circuit, a
second lead for connection to the output of the control unit, a
third lead for connection to the one of the pair of ballast circuit
output leads connected to the ballast capacitance, and a fourth
lead for connection to the lamp in the luminaire. Such a module can
readily be retrofit into a luminaire. For each additional luminaire
in the HID lighting system, the respective slave unit is connected
to the ballast and lamp in the same manner and its second lead is
connected to the second lead of the prior slave unit in a serial
fashion.
According to yet another aspect of the invention, the control unit
includes input receiving means for receiving an input signal on a
single input line and switching control means responsive to the
input signal for switching the control relay.
These and other objects, features, and advantages of the invention
will become more apparent with reference to the accompanying
drawing, detailed description, and claims.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a simplified schematic diagram of a lighting system
having a plurality of HID lighting fixtures and a bi-level control
system in accordance with the invention which includes a common
control unit and a respective slave unit in each fixture;
FIG. 2 is a schematic of a control circuit and a slave circuit for
the control system illustrated in FIG. 1; and
FIG. 3 illustrates a slave unit for connection in an HID
fixture;
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 schematically illustrates a bi-level HID lighting system
according to the invention having a branch circuit 10 which
includes a plurality of HID lighting fixtures, or luminaires
F.sub.1 -F.sub.10. The branch circuit has a pair of input terminals
11, 12 to which a voltage, such as 277V or 120V, may be applied via
an AC utility line upon closing of breaker CB1 and includes a
common, neutral line and a line voltage line "V.sub.m " connected
to each of the fixtures for supplying electric power thereto. Each
of the fixtures includes an HID lamp 60 and a ballast 70 for
controlling the lamp operating current.
A bi-level control system 20 for operating the lighting fixtures at
a first light output level and a second, reduced output level
includes a respective slave unit 50 in each fixture and a control
unit 30 for controlling each of the slave units. The control unit
30 includes a pair of power supply inputs 31, 32 connected to the
common and line voltage lines of the branch circuit 10. Each slave
unit is connected to the ballast 70 and lamp 60 in its respective
fixture, to a control line from single output 33 of the control
unit 30, and to the common line of the branch circuit, as will be
described in greater detail with reference to FIG. 2. The control
system 20 also includes first and second occupancy sensors 40 and
45 which detect the presence or absence of a person within a
predetermined area lit by the lighting fixtures. The occupancy
sensors each have a pair of power supply terminals 41, 42; 46, 47
connected to power supply terminals 32, 36 of the control unit 30
and a respective single output 43; 48 connected to a respective
control input 34; 35 of the control unit.
As schematically shown in FIG. 2, the ballast 70 in each of the
fixtures F.sub.1 -F.sub.10 of FIG. 1 includes a conventional L-C
series circuit having a conventional choke B1, in the form of a
center-tapped transformer, and a ballast capacitor C1. The primary
coil B1.sub.p is connected at both ends to ballast circuit inputs
71, 72 which are in turn connected to the line voltage "V.sub.m "
and common lines of the branch circuit. The capacitor Cl is
connected between an end of the secondary coil B1.sub.s and an
output 73 of the ballast circuit. The other ballast output 74 is
connected to the other end of primary B1.sub.s. The ballast 70 is
conventional and may be, for example, an Advance Transformer
Company Model 71A6091 ballast. When connected in a normal fashion
to lamp 60 (without the control system according to the invention)
the transformer B1 and capacitor Cl operate the lamp at a full
rated output light level.
The slave unit 50 (of the control system 20) associated with each
fixture includes capacitance switching means comprised of a
switched slave capacitor C2 and a relay RLY1. The relay RLY1 is an
electro-mechanical relay having switch contacts and a switch member
55 moveable between a first, normally closed switch position and a
second, open switch position by coil 56. Capacitor C2 has one end
connected to ballast output 73, which is connected to capacitor C1,
and its other end connected to switch terminal 52 of relay RLY1 and
a lamp terminal of lamp 60. A surge suppressor RT1 is connected at
a junction between ballast output 73 and capacitor C2 and to relay
switch terminal 51. The surge suppressor is preferably in the form
of a choke, but may also be a negative temperature coefficient
(NTC) device. The relay RLY1 further includes control inputs 53, 54
for coil 56 connected, respectively, to the control line and to the
common line via ballast output 74.
The HID lamp 60 is connected to a junction between the capacitor C2
and switch terminal 52 and to the common line via ballast output
74. The HID lamp 60 may be, for example, a high pressure sodium
(HPS) lamp, a metal halide lamp, or a mercury vapor lamp.
In the normally closed switch position of relay RLY1 shown in FIG.
2, the slave capacitor C2 is shunted so that only the ballast
capacitor C1 is in series with the lamp 60. When the switch member
55 is moved to the open switch position by coil 56, the capacitor
C2 is not shunted and is in series with the lamp 60, the choke B1
and the ballast capacitor C1. With capacitor C2 in series with
capacitor C1, lamp 60 will operate at a reduced energy saving light
output level as compared to a full light output level when
capacitor C2 is shunted.
The control unit 30 which controls each of the slave units includes
a regulated power supply circuit 310 and control means comprised of
a timing means 330, switching control means 350 and switching means
390.
The regulated power supply 310 provides a regulated 5V DC level on
outputs 328, 329. It includes a transformer T2 which steps down a
120 volt input received on the power supply inputs 31, 32 to 9V.
Whenever the mains voltage Vm is at a level other than 120 volts,
transformer 300 may be used, which provides a voltage of 120V at a
pair of output terminals 302, 303. Fuse F1 is connected between
output terminal 302 of transformer 300 and input terminal 31 of the
regulated power supply and is selected to protect the control unit
from damage by excessive current draw. A surge suppressor D6
connected between input terminals 31, 32 is selected to protect
against voltage transients. A full wave bridge, connected across
the secondary winding T2.sub.s of transformer T2, consists of
diodes D1-D4. The cathode of diodes D2, D3 are connected to each
other at a junction 313 and the anodes of diodes D1, D4 are
connected to each other at junction 314, which is connected to the
first output 328 of the regulated power supply 310. The anode of
diode D2 and the cathode of diode D1 are connected at a junction
316 which is connected to one side of the secondary winding
T2.sub.s and the cathode of diode D4 and the anode of cathode D3
are connected to a junction 315 which is connected to the other
side of secondary winding T2.sub.s. The full wave bridge rectifies
the AC signal received on inputs 31, 32 into a DC signal with
ripple.
A commercially available voltage regulator VR1 (such as a model
LM7805 available from National Semiconductor), supplies a 5V DC
voltage. Input 317 is connected to junction 313 and output 319 is
connected to the other output 329 of the regulated power supply
circuit 310. One side of each of capacitors C3 and C4 are connected
between junction 313 of the full wave bridge and input 317 of
voltage regulator VR1. The other side of the capacitors C3, C4 are
connected to output 328, ground terminal 318 of voltage regulator
VR1, and one end of capacitor C5. The other end of capacitor C5 is
connected between output 319 of the voltage regulator VR1 and
output 329 and is selected to reduce noise on outputs 328, 329.
Capacitors C3 and C4 are selected to smooth out the ripple and
produce a constant DC level on outputs 328, 329.
Timing circuit 330 includes a commercially available precision
timer PT1, such as a model LM3905 available from National
Semiconductor, which is an integrated circuit with eight terminals
331-338 in the form of an eight-pin DIP. Resistor R1 and resistor
R2 are connected in series between the voltage reference terminal
332 and the R/C terminal 333 of timer PT1. Capacitor C6 has one end
connected to a junction between terminal 333 and resistor R2.
Capacitor C7 has one end connected to an end of resistor R1 and
terminal 332. Its other end is connected to output 328 of the
regulated power supply 310, the other end of capacitor C6 and
ground terminal 334, trigger terminal 331, logic terminal 338 and
emitter terminal 337 of timer PT1. Resistor R3 has one end
connected to the V' terminal 335 and output 329 of the regulated
power supply and the other end connected at a junction between the
collector terminal 336 and output 339 of timing circuit 330. The
capacitor C7 is selected to reduce noise in the timing circuit so
the r-c time constant is not influenced by circuit noise. The value
of capacitor C6 determines when the collector terminal 336 is
switched from a logic zero level to a logic high level.
Switching control circuit 350 includes a first control input 34 for
receiving an input signal from a first input, such as occupancy
sensor 40 shown in FIG. 1, and a second control input 35 for
receiving a second control input, such as from a second occupancy
sensor 45. Control input 34 includes two input terminals 351, 352
and control input 35 includes two input terminals 361, 362.
Connected to each of the pairs of input terminals is respective
optoisolator OI1, OI2. The optoisolators are conventional and may
be, for example, a Harris Electronics Model H11AA1 which can
receive both AC and DC signals on inputs 34, 35.
Input terminals 352 and 362 are connected directly to the inputs
354, 364 of the respective optoisolators. A respective resistor R4,
R5 is connected between each of the terminals 351, 353; 361, 363.
The resistors R4 and R5 limit the current from the input devices
and set the detection range of the optoisolators, OI1 and OI2. By
careful selection of R4 and R5, a wide range of AC or DC voltages
(other than 120 volts) can be detected by OI1 and OI2. The output
terminals 355, 365 of optoisolators OI1, OI2 are each connected to
a respective junction 357, 367 connecting one end of each of
capacitor C8 and resistor R6 and capacitor C9 and resistor R7. The
other end of capacitors C8, C9 are connected to respective
terminals 356, 366 of the optoisolators, to the terminals 331, 334,
337 and 338 of timer PT1 and to an end of capacitors C6, C7. The
other end of resistors R6, R7 are connected at a common junction
connected to resistor R3 and terminal 335 of the timing circuit
330. The resistors R6 and R7 limit the current for the output of
OI1 and OI2 and function as pull-up resistors, driving the output
of OI1 and OI2 high whenever an input signal does not exist. The
capacitors C8 and C9 filter the ripple and stabilize the output of
OI1 and OI2.
The control circuit 350 further includes logic (NAND) gates N1-N4
which are embodied by a 14 pin integrated circuit. The two inputs
358, 368 for NAND gate N2 are connected, respectively, to junction
357 between resistor R6 and capacitor C8 and to junction 367
between capacitor R7 and capacitor C9. Both inputs 370, 371 of gate
N3 are connected to the output 369 of gate N2. Gate N1 has one
input 373 connected to output 339 of the timing circuit 330 and its
other input 374 connected to output 372 of gate N3. Gate N4 has
both inputs 376, 377 connected to output 375 of gate N1. Terminals
379, 380 of gate N4 represent the power supply terminals for the
integrated circuit and are connected to the common and 5V DC lines
from the outputs 328, 329 of power supply circuit 310. The NAND
gates N3 and N4 act as inverting buffers for the output signals
from the NAND gates N1 and N2 and insure that the signals from
optoisolators OI1 and 012 are decoded properly.
Switching circuit 390 includes a single control output 33 of
control unit 30, connected via fuse F2 and a single control line to
control terminal 53 of slave relay RLY1. Inputs 391 and 394 are
power supply inputs connected to the 5V DC and common lines. Input
392 is connected to output 378 of gate N4 and control circuit 350.
Resistor R8 has one end connected at a junction to base B of
transistor Q1 and input 392. The other end of resistor R8 is
connected to input terminal 391, the cathode of diode D5, one side
of capacitor C10, and input terminal 395 of control relay RLY2. The
anode of diode D5 is connected to the other input terminal 398 of
relay RLY2 and to the collector of transistor Q1. The emitter of
transistor Q1 is connected to the other end of capacitor C10 and
power supply terminal 394. Relay RLY2 is an electro-mechanical
relay having switch contacts and a switch member 399 moveable
between a first, normally open switch position shown in FIG. 2 and
a second, closed switch position, by coil 400. Relay switch
terminal 397 is connected to the line voltage input terminal 31 of
voltage regulating circuit 310 and switch terminal 398 is connected
to output 33 of the switching circuit and control unit.
The operation of the control system is as follows. When "mains"
circuit breaker CB1 of the branch circuit 10 is closed, voltage Vm
is supplied to the ballasts 70 of fixtures F.sub.1 -F.sub.10 via
ballast inputs 71, 72 and to the control unit 30 at power supply
inputs 31, 32. Switch member 55 of the slave relay RLY1 is in its
normally closed position (providing a conductive path between
terminals 51, 52) with coil 56 in an un-energized state. When
breaker CB1 closes, current flows through the surge suppressor RT1,
across the closed switch contacts of relay RLY1, and ignites the
lamp. It should be understood that either ballast 70 or the lamp
includes a conventional ignitor (not shown) which provides a
sufficient starting pulse to start the lamp. The switched, slave
capacitor C2 is shunted and is not in the lamp-ballast circuit.
Transformer B1 and capacitor C1 of ballast 70 regulate lamp current
to the required level for full light output.
The application of voltage to the timing circuit 330 upon closing
of breaker CB1 via the regulated voltage supply circuit 310 begins
the timing sequence. As the timing sequence begins, the output 336
of the precision timer PT1, and thus output 339 of timing circuit
330 is at a logic zero level. The output 339 remains at this zero
level until the capacitor C6 charges to a sufficient level to cause
the output 336 of PT1 to switch to a high logic state. The
capacitance of capacitor C6 is selected such that the output of
timer PT1 does not switch to the high logic state until the HID
lamp 60 has reached a steady, full light output level. This
prevents the HID lamp from being switched to a reduced light-output
level until the lamp is fully warmed up. As long as the output 336
of PT1, (and thus input 373 of logic gate N1) is at logic zero, the
logic gate N1 is disabled which prohibits the output 375 of logic
gate N1 from changing states no matter what state the other input
374 might be. With logic gate N1 disabled, its output 375 and
inputs 376, 377 of gate N4 are at a logic high level, making output
378 a logic low.
The resistor R8 is used as a pull-up resistor for the output of N4.
Whenever the output 378 of logic gate N4 is at logic low, the
transistor Q1 is off, preventing the coil 400 of relay RLY2 from
energizing and keeping switch member 399 in its normally open
position. In this normally open position of RLY2, no control signal
is applied to coil 56 of RLY1 over the control line and the lamp 60
remains at full light output level.
When the precision timer PT1 reaches the desired time delay from
the initial closing of circuit breaker CB1, the output 336 of PT1
is switched off which causes the resistor R3 to pull the output 336
to a logic high level. This enables the logic gate N1 to be
controlled by the output 372 of the logic gate N3.
When an input signal (such as from an occupancy sensor 40 or 45 in
FIG. 1, or a wall switch, photocell, infrared sensor, etc.) is
applied to either control input 34 (terminal 351, 352), control
input 35 (terminals 361, 362), or both, a low logic level signal
appears on the outputs (junctions 357, 367) of optoisolator OI1
and/or OI2. A low logic level on either junction 357, 367 or both,
seen at inputs 358, 368 of gate N2, makes output 369 of NAND gate
N2 a logic low. This makes inputs 370, 371 of gate N3 low and
output 372 of gate N3 high. With input 373 also high because of PT1
having reached its designated delay time, and input 374 high, the
output 375 and inputs 376, 377 of gate N4 will be low. This makes
output 378 high.
When the logic high signal is applied form output 378 of gate N4 to
the base of the transistor Q1, the coil 400 of relay RLY2 is
energized which closes the contacts across terminals 397, 398. This
provides a control signal on the control line and energizes coil 56
of slave relay RLY1 by completing a circuit from input 31 of
regulated power supply 310 (which is at line voltage Vm) across
switch contacts 397, 398 of RLY2 over the control line to terminal
53 of RLY1, through coil 56 to terminal 54, which is connected to
the common line of branch circuit 10. With coil 56 of relay RLY1
energized, switch member 55 is moved to its open position and
allows the capacitor C2 to enter the lamp-ballast circuit in series
with capacitor C1, ballast B1 and lamp 60. The capacitor C2 is
selected to bring the lamp 60 to the desired low, stable and energy
saving level.
When the input signal is removed from the control input 34 or 35 to
which it was applied, and there is no input signal on either of the
control inputs 34, 35, the output 378 of logic gate N4 again
becomes logic low and the transistor Q1 is switched off. With coil
400 now un-energized, the switch member 399 moves to its normally
open position and the circuit from power supply input 31, through
relay RLY2, input 53 and coil 56 of relay RLY1 in the slave units
is opened, and switch member 55 moves back into its normally closed
position.
Movement of switch member 55 into its normally closed position
places the surge suppressor RT1 back into the circuit where it can
clamp the high inrush current from the discharging capacitor C2,
protecting the switch contacts of relay RLY1 and adjacent
components from damage from high current spikes. In the switching
circuit 390, the diode D5 serves as a discharge path for coil 400
of the relay RLY2 and prevents voltage transients from feeding back
onto the DC supply line connected at inputs 391, 394. The capacitor
C10 functions as a bypass capacitor by filtering noise form the DC
supply line. The fuse F2 protects the output 33 of control unit 30
from over current conditions caused by a short circuit on the
control line.
The capacitor C2, surge suppressor RT1, and the relay RLY1 of slave
unit 50 are preferably potted in a plastic capacitor housing 150
(such as a Model $2 can, make Advance Transformer Company) and are
installed in a fixture as a complete module M1 (FIG. 3). This
module has only four wires, which makes the module easy and fast to
retrofit into a fixture containing a lamp 60 and ballast 70. A
first wire 151 (white) is used to connect the terminal 54 of the
slave relay to the common, neutral line of the branch circuit. A
second wire 152 (blue) connects the terminal 53 of the slave relay
to the single control line, which is connected to output 33 of the
control unit. A third wire 153 (black) is used to connect the slave
capacitor C2 to the ballast lead wire connected to the ballast
capacitor C1 and the fourth wire 154 (black/white) connects the
other side of slave capacitor C2 and to a terminal of the discharge
lamp. The above components can also be potted in an aluminum
capacitor can or various ballast housings depending on the size
constraints of the lighting fixture.
The slave unit in the form of module M1 can easily be retrofit into
a fixture by removing the ballast lead which is connected
internally to the ballast capacitor C1 from one of the lamp
terminals. This ballast lead is then connected to the black lead
from module Mi. The black/white lead is then attached to the one
lamp terminal. The white lead is then attached to the common line
along with the white lead of the ballast, and the blue lead is
attached to the control line coming from output 33 of the control
unit.
The series configuration of the fixture capacitor C1 and the slave
capacitor C2 with the ballast capacitor C1 reduces the physical
size of capacitor C2 because a lower voltage rated part may be used
than if they were arranged in parallel. A small size for the
ballast module M1 is important because of the limited space
available in a fixture. If C1 and C2 are used in a parallel
configuration, C2 must be rated at the same voltage level as C1
which forces C2 to be physically larger than in the series
connection. For example, for a 400 watt metal halide lamp, C1 and
C2 would both be 400 volt parts in a parallel circuit configuration
whereas C1 is a 400 volt part and C2 is a 120 volt part in the
series circuit shown in FIG. 2.
The series connection of C1 and C2 also allows the contacts of
relay RLY1 to be rated at a lower voltage than it would be if it
were used in the parallel configuration. (120 volt contact rating
for a series circuit and 400 volts for the parallel circuit). This
also reduces the physical size of the relay, permitting a smaller
module M1 than if a parallel configuration were used. In the module
shown in FIG. 3 the housing 151 had dimensions of 124.2 mm
.times.47.2 mm. The dimensions of capacitor C2 was 57 mm
.times.38.6 mm for a 40 .mu.f, 120 v. The relay RLY1 was a Potter
and Brumfield kup series with dimensions of 55.2 mm .times.46.7
min.
The series configuration of capacitors C1 and C2 also lessen the
effect of inrush currents when C2 is switched out of the circuit.
The hazards of high surge currents are more pronounced in a
parallel configuration.
In the control system shown in FIG. 1, the control unit 30 is
powered directly from the branch circuit 10 it controls. This
insures that the controller timing circuit 330 is initiated every
time power is applied or restored to the lighting fixtures. Also,
this enables the use of only one control wire from the output 33 of
the control unit to slave relay RLY1 in the lamp fixtures as the
common line is shared by the slave unit and the ballast. This
simplifies the installation or addition of the module M1 into an
existing fixture and reduces wiring as compared to the known
systems.
As previously mentioned, the optoisolators 011 and 012 are capable
of sensing AC or DC current. By careful selection of resistors R4
and R5, a wide range of AC or DC voltages may be used as inputs to
the controller. This enables the controller to interface with
virtually all types of sensing or switching devices such as:
occupancy detectors, infrared sensors, photocells, proximity
switches, wall switches, etc., which may supply its control signal
at levels other than 120 volts. It can also be interfaced to a
personal computer or a computerized time clock.
The external occupancy sensors 40, 45 are directly powered from the
control unit 30. This insures that the sensors are operational
whenever the controller receives power. This further simplifies
wiring as neutrals can be shared; therefore, only one control wire
is needed to be brought to the inputs 34, 35 of the control unit
from the outputs 43, 48 of the sensors 40, 45. The other sensor
outputs 44, 49 are connected back to their respective common lines
connected at inputs 42, 47. The single control wire would be
connected to terminals 351, 361 of control inputs 34, 35 of the
control unit. The other terminals 357, 362 are then tied back to
the common line within the control unit 30, for example, at input
32.
Since the control inputs to the controller are "floating" and
isolated, the sensors may also be connected to a different branch
circuit than the contoller or can be out of phase with respect to
the phasing of the controller.
The timing circuit of the controller can be made adjustable by
changing the capacitance of capacitor C6 so the timing interval is
compatible with the type of lamps being controlled (i.e. metal
halide, mercury vapor or sodium).
The following Parts Table lists components used int eh circuit of
FIG. 2 for 400 watt metal halide lighting fixtures.
PARTS TABLE ______________________________________ PARTS PART
DESCRIPTION ______________________________________ R1,2 3.6M, 5%,
1/4W R3,6,7 10K, 5%, 1/4W R4,5 20K, 5%, 5W R8 470 OHM, 5%, 1/4W C1
SELECTED WITH BALLAST BL TO OPERATE LAMP AT FULL POWER (i.e.: 400W
MH LAMP-24 uF, 400V) C2 SELECTED TO DIM LAMP TO DESIRED LEVEL
(i.e.: 40 uF 120V) C3,4 100 uF, 20%, 16V C5 1 uF, 20%, 25V C6 100
uF, 20%, 10V C7,10 .1 uF, 20%, 550V C8,9 22 uF, 20%, 6.3V D1-D5 1A,
50V D6 SURGE ABSORBER, 220V VR1 5V REGULATOR (National
Semiconductor, Model LM7805) PT1 PRECISION TIMER (National
Semiconductor, Model LM2905) OI1,2 OPTOISOLATOR (Harris
Electronics, Model H11AA1) N1-N4 QUAD 2-INPUT NAND GATE (National
Semiconductor, Model 7400N) Q1 NPN 30V 1.5W TRANSISTOR (2N222) RLY1
SPDT 120VAC 30A RLY2 SPDT 5VDC 10A T1 OPTIONAL 277V:120V T2 120V:9V
RT1 CHOKE COIL OR INRUSH CURRENT LIMITER (Negative Temperature
Coefficient) ______________________________________
While there have been shown to be what is presently considered to
be the preferred embodiment of the invention, it will be apparent
to those of ordinary skill in the art that various modifications
can be made without departing form the scope of the invention as
defined by the appended claims.
For example, while the circuit of FIG. 2 and the components listed
in the Parts Table above are for 400 watt metal halide lighting
fixtures the bi-level lighting control with shared neutrals can be
modified to control various wattages of metal halide lamps as well
as other gaseous discharge lighting sources such as mercury, high
pressure sodium, and fluorescent which utilize constant wattage
autotransformer (CWA) and (CWI) ballast circuits. The design shown
above is for the control of ten lighting fixtures (based on a 277
volt branch circuit). Other lamp types and other wattages will
dictate the total number of lamp fixtures that can be controlled on
the branch circuit. The final determinating factor will be the
total wattage or loading on the branch circuit breaker.
* * * * *